1. Field of the Invention
The invention relates to a catalyst unit for an exhaust gas catalytic converter. The invention, furthermore, relates to an exhaust gas catalytic converter and to a method for producing a catalyst unit for an exhaust gas catalytic converter.
2. Description of the Prior Art
Exhaust gas catalytic converters for large engines, such as for example for stationarily operated large diesel engines or diesel engines of ships typically comprise a plurality of catalyst units. Each catalyst unit comprises a ceramic catalyst body and a metallic housing through which exhaust gas flows, which at least in some portions surrounds the catalyst body seen perpendicularly to the through-flow direction of the same. The ceramic catalyst body of a catalyst unit is also described as a honeycomb and the housing of a catalyst unit also as a canning.
A ceramic catalyst body for a catalyst unit has tolerances in the range of a plurality of millimeters due to production tolerances. The metallic housings however have to have a defined outer cross section or a defined outer contour to ensure an optimal connection of the catalyst units to other assemblies of an exhaust gas system of the internal combustion engine, for example two lines conducting exhaust gas or two reactor housings. For this reason, at least one bearing mat is positioned between the catalyst body and the housing for catalytic converter, an exhaust gas catalytic converter having such a catalyst unit and a method for producing such a catalyst unit.
According to one aspect of the invention, the catalyst body is held in a force-fit manner in the housing via a press fit perpendicularly to the through-flow direction of the same subject to the intermediate arrangement of the or each bearing mat namely in such a manner that seen in through-flow direction of the catalyst body the press fit between the housing and the catalyst body is exclusively formed in defined axial positions. In the defined axial positions the housing comprises groove-like recesses for reducing the inner cross section of the housing in some sections, and wherein the press fit between the housing and the catalyst body is exclusively formed in the region of the groove-like recesses.
With the present invention it is proposed, for the first time, to hold the catalyst body of a catalyst unit, which has tolerances due to production, subject to the intermediate arrangement of at least one bearing mat via a press fit in the housing in a force-fit manner such that the press fit seen in through-flow direction of the catalyst body is exclusively formed in defined axial positions. To this end, the housing comprises groove-like recesses for the reduction of the inner cross section of the housing in some sections in the defined axial positions, wherein the press fit between the housing and the catalyst body is formed exclusively in the region of these groove-like recesses. Between the groove-like recesses the housing seen in the flow direction of the catalyst body has a defined outer cross section, as a result of which connecting the catalyst unit or an exhaust gas catalytic converter comprising at least one catalyst unit to other assemblies of an exhaust gas system of an internal combustion engine is then possible without problems.
In particular when providing an exhaust gas catalytic converter for a large engine comprising a plurality of catalyst units arranged in through-flow direction parallel next to one another, a simple connection of the exhaust gas catalytic converter to other assemblies of an exhaust gas system of the large engine is thereby possible.
According to an advantageous further development, at least one bearing mat is positioned between the catalyst body and the housing seen in through-flow direction of the catalyst body exclusively in the region of the groove-like recesses of the housing. In particular when the or each bearing mat is exclusively positioned in the region of the groove-like recesses of the housing between the catalyst body and the housing, the use of such bearing mats can be significantly reduced compared with the prior art. Because of this it is possible to reduce production costs of a catalyst unit.
According to a further advantageous further development, clearances are introduced into the housing seen in through-flow direction of the catalyst body downstream of the first groove-like recess and upstream of the last groove-like recess. Because of this it is possible to produce a catalyst unit with low weight, using little material and thus lower costs.